[PATCH nf-next v2] netfilter: nft_quota: match correctly when the quota just depleted

[PATCH nf-next v2] netfilter: nft_quota: match correctly when the quota just depleted

[Zhongqiu Duan]

The xt_quota compares skb length with remaining quota, but the nft_quota
compares it with consumed bytes.

The xt_quota can match consumed bytes up to quota at maximum. But the
nft_quota break match when consumed bytes equal to quota.

i.e., nft_quota match consumed bytes in [0, quota - 1], not [0, quota].

Fixes: 795595f68d6c ("netfilter: nft_quota: dump consumed quota")
Signed-off-by: Zhongqiu Duan <dzq.aishenghu0@gmail.com>
---
v2:
- Keeps the behavior of notified on the quota just exhausted.
- Convert to a more descriptive title.
v1: https://lore.kernel.org/netfilter-devel/20250410071748.248027-1-dzq.aishenghu0@gmail.com/

 net/netfilter/nft_quota.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/net/netfilter/nft_quota.c b/net/netfilter/nft_quota.c
index 9b2d7463d3d3..df0798da2329 100644
--- a/net/netfilter/nft_quota.c
+++ b/net/netfilter/nft_quota.c
@@ -19,10 +19,16 @@ struct nft_quota {
 };
 
 static inline bool nft_overquota(struct nft_quota *priv,
-				 const struct sk_buff *skb)
+				 const struct sk_buff *skb,
+				 bool *report)
 {
-	return atomic64_add_return(skb->len, priv->consumed) >=
-	       atomic64_read(&priv->quota);
+	u64 consumed = atomic64_add_return(skb->len, priv->consumed);
+	u64 quota = atomic64_read(&priv->quota);
+
+	if (report)
+		*report = consumed >= quota;
+
+	return consumed > quota;
 }
 
 static inline bool nft_quota_invert(struct nft_quota *priv)
@@ -34,7 +40,7 @@ static inline void nft_quota_do_eval(struct nft_quota *priv,
 				     struct nft_regs *regs,
 				     const struct nft_pktinfo *pkt)
 {
-	if (nft_overquota(priv, pkt->skb) ^ nft_quota_invert(priv))
+	if (nft_overquota(priv, pkt->skb, NULL) ^ nft_quota_invert(priv))
 		regs->verdict.code = NFT_BREAK;
 }
 
@@ -51,13 +57,13 @@ static void nft_quota_obj_eval(struct nft_object *obj,
 			       const struct nft_pktinfo *pkt)
 {
 	struct nft_quota *priv = nft_obj_data(obj);
-	bool overquota;
+	bool overquota, report;
 
-	overquota = nft_overquota(priv, pkt->skb);
+	overquota = nft_overquota(priv, pkt->skb, &report);
 	if (overquota ^ nft_quota_invert(priv))
 		regs->verdict.code = NFT_BREAK;
 
-	if (overquota &&
+	if (report &&
 	    !test_and_set_bit(NFT_QUOTA_DEPLETED_BIT, &priv->flags))
 		nft_obj_notify(nft_net(pkt), obj->key.table, obj, 0, 0,
 			       NFT_MSG_NEWOBJ, 0, nft_pf(pkt), 0, GFP_ATOMIC);
-- 
2.43.0

Re: [PATCH nf-next v2] netfilter: nft_quota: match correctly when the quota just depleted

[Pablo Neira Ayuso]

On Thu, Apr 17, 2025 at 03:49:30PM +0000, Zhongqiu Duan wrote:
> The xt_quota compares skb length with remaining quota, but the nft_quota
> compares it with consumed bytes.
> 
> The xt_quota can match consumed bytes up to quota at maximum. But the
> nft_quota break match when consumed bytes equal to quota.
> 
> i.e., nft_quota match consumed bytes in [0, quota - 1], not [0, quota].

Yes, quota is off by one.

Applied to nf-next, thanks.